Does anyone know what the maximum total timing is for a 1971 455 with flattop piston, Edelbrock heads, comp cams xe 284h cam? My new build likes 22-24 degrees initial. At that it does not ping and the power seems good. I currently have my vacuum advance connected to manifold vacuum as it idles better with more advance but if I go more than 22-24 degrees base it pings on acceleration. I rebuilt the HEI distributor and put in an MSD recurve kit in. I currently have the heaviest springs available installed in my distributor. This makes my centrifugal advance limited to 18 degrees but it comes in very late. I would like to put the lighter springs in and see what happens. It is possible that if I put the lighter springs in i could be running up to 48 degrees without vacuum advance. My vacuum advance canister is currently limited to 10 degrees so I could hit up to 58 degrees theoretically.

Just looking at if I can go ahead with lighter springs or if i need to weld my dist to limit the travel of the centrifugal advance. Thanks.

 

I would try lighter springs, but do your changes one at a time and in steps. Try the medium springs too, or a combo of light med. as well.

I'm thinking that eventually your initial will need to come down.

Sounds like a nice combo.

 

I have tried to bring my timing down below 22 degrees of initial but it does not like to idle below that.

 

If your going to fine tune your timing I'm going to suggest doing it on the dyno. Your not going to advance your timing much more than where you have it now without detonation on pump gas. The general rule of thumb is 36-38 total and 50-52 with vacuum. I've seen engines that can tolerate a bit more and a lot of engines that could not. I will also add that setting an engine for wot peak power may not be able to run on the street with fluctuations in fuel quality and changes in atmospheric conditions.

 

Apparently you need a different center bar and weights. The contours of these parts is what dictates the amount of total advance. If you are using the springs to limit the advance at a particular RPM, be aware that as the RPM increases beyond that amount the advance will continue to increase. This is essentially what you are seeing when the lighter weights are installed. With the correct center bar and weights, the springs will change the RPM at which the total advance is reached, but not the amount of advance.

Do you know what center bar and weights you have? If they are GM parts, there will be a number stamped on them. The center bar/weight number combos can be looked up to see how much mechanical advance they give.

 

I echo what is said here. I will add that the best advice IS the dyno. That way you can super tune both the fuel and ignition curves at the same time. Money well spent for a dyno session with a good dyno tech. Both fuel and ignition need to play nice together to extract all the potential from your set up.
But before you do that send the dist out to someone who can professionally set the timing curve to your cam compression, heads, stall and rear gear specs. The aluminum heads will tolerate a touch more advance.
20-24 base sounds high to me. Generally a 10-11:1 engine 400/425/455 with a decent cam likes 12-14 initial. Then depending on the cam another 10-14 on the vac canister at idle on unported intake vacuum . Then the rest all in by 28-3000RPMs. So a grand total of 38-42ish for pump gas. It must all work together. Your kind of guessing at the curve. FYI You can put 2 different tension springs to achieve a custom curve. The advance stops need to be considered too as mentioned especially if its a smog era advance curve. It will be way out of whack for a hiperf engine.
To answer your question the max timing an engine can take all depends on the above items. Youll know when its too much as you will induce detonation, hard starting and rough idle.

 

Thank you for the information guys. The weather has been poor here so tonight was the first day I was able to get the car out again.

I am running an MSD center bar and weights in a stock GM HEI unit. I went to the medium set of springs from the heavy ones tonight. The car did not respond well to the 2 medium ones. At lower rpm cruise, about 1500-2000rpm the car was surging. I also noted a slight ping when I accelerated hard from low rpm. I swapped out one of the medium springs for a heavy one and will try again tomorrow with one heavy and one medium.

I would love to get the car on a dyno sometime in the next couple of months but at this point I just want to get the car driveable for now.

 

The heavy springs may be keeping your timing from fully advancing at lower rpms. Then when you install the lighter ones it may be allowing the advance to go more, therefore pinging and surging. I would disconnect the vacuum advance while your testing as it may be exceeding what your engine can tolerate. When you make changes you should hook up a timing light and note what your total timing is doing prior to going for a ride.

 

I agree with the above. I am not familiar with the MSD curve kit, but I know the Moroso kit's center bar and weights allow 24º of mechanical advance, so the initial needs to be set to 10-12º to achieve 34-36º total advance. If your kit is the same and your initial is 22-24º then your total is 46-48º, which would explain why you need the stiffest springs to prevent pinging upon acceleration - you are effectively using the spring tension in an attempt to limit the total amount of mechanical advance.

I recommend you use either timing markers on the balancer or a dial back timing light to map your advance. I did this by installing the stiffest springs so there was no advance at idle, recorded that amount, the removed the springs completely so the mechanical advance came in at very low RPM, and recorded that amount. This allowed me to measure exactly how much mechanical advance my center bar and weights gave, and I was then able to set the initial appropriately. After that I played with the springs to get the advance all-in at the RPM that worked best.

What I eventually ended up with was ditching the aftermarket weights and center bar in favor of the factory parts, which gave ~16º mechanical advance so I was able to set the initial to ~20º instead of 12º. I also ended up with one light and one medium spring from the kit.

 

What is the Octane rating on the gas you are using? What is the engine temperature when testing? Here are few other thoughts too compare notes: My 455 has true 10.5 compression ratio with Cometic head gaskets, running 93 octane, Comp Cams little milder than yours, extreme energy 274, Edelbrock heads etc. With an Suburban aluminum radiator, Mr Gasket adjustable thermostat, my engine runs a cool 155-180 degrees, maybe 185 in Texas heat. That said keeping the engine running on the cooler side maybe allowing me to run 20 degrees initial timing and 36 degrees total without vacuum on a stock GM HEI. No pings at all, motor will pull your shirt off on launch! Or maybe I'm just lucky